Positron Emission Tomography (PET) is fundamentally different from SPECT because it relies on coincidence detection rather than mechanical collimation. PET imaging is based on positron (β⁺) decay, in which the emitted positron annihilates with an electron, producing two 511 keV photons travelling in approximately opposite directions. These photons are detected simultaneously by opposing detectors, allowing precise localisation along a line of response.

PET systems use ring detectors composed of scintillation crystals such as LSO, LYSO, or BGO coupled to photodetectors. Coincidence timing circuits identify true, random, and scatter events. Time-of-flight (TOF) technology further improves signal localisation and signal-to-noise ratio by measuring the small timing differences between detected photons. Compared with SPECT, PET offers higher sensitivity and improved spatial resolution due to electronic rather than physical collimation.

PET physics is examined in FRCR Part 1, ABR Core, RANZCR, and FC(Rad) Diag SA physics assessments. Common topics include coincidence detection principles, random and scatter correction, attenuation correction using CT, partial volume effects, spatial resolution determinants, and quantitative accuracy (including SUV calculation and recovery coefficients). Questions often require understanding the physical origin of artefacts and limitations in quantitative imaging.

The questions in this section cover annihilation physics, coincidence detection, detector materials, time-of-flight principles, reconstruction algorithms, quantitative imaging, and factors influencing spatial and contrast resolution. These board-level problems are designed to consolidate your understanding of PET as both a physical system and a quantitative imaging modality.

The questions covered here provide a good framework to build from. Get access to over 2,000 board-level radiology physics questions with highly detailed explanations, structured feedback, and exam-focused learning tools. Explore the complete question bank here.